1. Field of the Invention
The present invention relates to a camera, and a method of discerning status of a photo film cassette. More particularly, the present invention relates to a camera in which one of used statuses of photo film contained in a photo film cassette can be discerned reliably according to a position of a data disk in the photo film cassette, and a method of discerning one of used statuses of the photo film contained in the photo film cassette.
2. Description Related to the Prior Art
There is a known photo film cassette of a type IX240, for example FUJICOLOR NEXIA manufactured by Fuji Photo Film Co., Ltd. This type IX240 is characterized in that rotation of a spool causes photo film to advance to an outside of a shell of the cassette through a photo film passage port. In the photo film cassette, the photo film passage port contains a cassette shutter member which is rotatable to open and close the photo film passage port, and when the passage port is closed, operates for blocking ambient light, instead of light-trapping fabric which is conventional in the field of photo film cassettes. The photo film cassette also has a data disk, on which a rotary bar code is printed. Various kinds of information, including photo film speed and the number of available frames, are represented by the rotary bar code.
The data disk is rotatable with the spool. The rotary bar code is constituted by a bar code portion and a quiet zone. The bar code portion consists of a combination of plural black bars and plural white bars alternately arranged. The black bars have low reflectance, and have black or other dark color. The white bars have high reflectance, and have white, silver or other light color. The quiet zone has a sufficiently great central angle with the low reflectance, and operates to define beginning and closing ends of the bar code portion. Immediately after insertion of the photo film cassette into a camera, the spool is rotated. During the rotation, the rotary bar code is read by a photo sensor of the camera through a first opening for reading data or a second opening for discernment of used statuses.
In the photo film cassette, it is impossible to discern any of unexposed, partially exposed, all exposed and developed statuses of the photo film only with appearance of the photo film cassette, because all the photo film is contained in the cassette shell. There is a known construction in which the camera has the photo sensor to read the rotary bar code for discerning one of the used statuses for the purpose of avoiding an exposure-taking operation with the photo film cassette having the exposed or developed status. A portion of the rotary bar code to appear in the second opening is predetermined according to each of the used statuses.
The photo film cassette is unloaded from the camera after finishing rewinding the photo film. If the photo film cassette contains the photo film being exposed, the spool is controlled to stop for the quiet zone to exist in the second opening. If the photo film cassette contains the photo film being unexposed, the spool is oriented for the bar code portion to exist in the second opening. To avoid accidental deviation of the position of the spool, a spool lock mechanism operates for blocking rotation of the spool while the cassette shutter member closes the photo film passage port.
In the camera, a spool drive shaft is engaged with the spool to rotate it. An opener drive shaft is engaged with the cassette shutter member to rotate it from the closed position to the open position. To reduce a size or the number of parts of the camera, a single motor is used in the camera for rotating both the spool drive shaft and the opener drive shaft. Partial rotation of the spool drive shaft is transmitted to the opener drive shaft. In the camera, the spool is rotated in an rewinding direction of the photo film for the purpose of reading the rotary bar code or detect a position of the rotary bar code upon the cassette insertion. The opener drive shaft is also rotated in the course of the rotation of the spool.
The spool drive shaft has an engaging projection, which is engageable with an axial key way formed in the spool. It is likely that a rotational position of the engaging projection is different from a rotational position of the key way of the spool, due to a difference between the status of a previously unloaded cassette and the status of the photo film cassette presently loaded. Thus the spool drive shaft has a construction slidable in an axial direction of the spool. Before its rotational position meets that of the key way, the spool drive shaft is pushed upwards from the spool against bias of a spring associated with the spool drive shaft. Upon meeting the position of the key way, the spool drive shaft becomes engaged with the key way.
To discriminate the used statuses of the photo film cassette, the number of borders each of which is defined between one of the white bars and one of the quiet zone and the black bars is counted after a start of rotating the spool drive shaft. According to the counted border number, it is determined which of the quiet zone and the bar code portion existed in the first or second opening at the time of cassette insertion. As a result the used status of the photo film in the photo film cassette is discerned.
There is a problem in that the used statuses are misread in the camera of which the motor is used for rotating both the cassette shutter member and the spool. There are various causes of this misreading. Firstly at the time of the cassette insertion, the spool drive shaft is not oriented for meeting a position of the spool. Secondly a lock gear of the above-mentioned spool lock mechanism is rotated forcibly in spite of existence of a protruding portion of the lock lever of the spool lock mechanism within the path of the lock gear. Thirdly the spool drive shaft rotates the opener drive shaft before opening the cassette shutter member. Those phenomena create failure in reading by use of the photo sensor, as the data disk with the spool makes abnormally instable motion, for example abrupt reciprocal rotations in a small range or a provisional stop.